Use of microcapsules in gypsum plasterboards

ABSTRACT

The invention relates to the use of microcapsules with latent heat storage materials as capsule cores on gypsum plasterboards, gypsum plasterboards containing the same and a method for production thereof.

[0001] The present invention relates to the use of microcapsulescomprising latent heat storage materials as capsule core inplasterboard, to the plasterboard in which they are present and to aprocess for producing this plasterboard.

[0002] An important focus of research for reducing energy requirementsand for utilizing available heat energy are latent heat storagematerials. They have a variety of uses, for example as heat transfermedia in heating and cooling systems or for the storage of heat ininsulation materials or building materials. Their function is based onthe enthalpy change associated with the solid/liquid phase transition,which results in absorption of energy from the surroundings or releaseof energy into the surroundings. They can thus firstly be used forkeeping the temperature constant within a prescribed temperature rangeand, secondly, can improve thermal insulation in a suitable arrangement.

[0003] DE-A 19 654 035 describes microcapsules as heat transfer medium.In these, the storage medium is surrounded by a capsule wall ofmelamine/formaldehyde resin.

[0004] Melamine/formaldehyde resin microcapsules are likewise disclosedin U.S. Pat. No. 5,456,852, although these have a specific storagemedium as core. However, such melamine/formaldehyde resin capsulesdisplay unsatisfactory hydrolysis stability over a prolonged period inthe transport medium, which is generally aqueous.

[0005] U.S. Pat. No. 4,747,240 teaches the use, in gypsum plaster, ofmacroencapsulated storage substances which have a particle size above1000 μm and whose capsule wall is a high-melting resin. However,capsules of this size require very thick walls to prevent them frombeing destroyed on mixing with the building materials.

[0006] EP-A-10 29 018 teaches the use of microcapsules having a capsulewall of highly crosslinked methacrylic ester polymer and a latent heatstorage core in building cements/plasters. Thus, the microcapsules canbe incorporated into gypsum plaster without influencing its properties.

[0007] An important building material is plasterboard. This is generallyused in interior finishing of buildings for lining walls and ceilings.In this sector, too, there is a desire to increase thermal insulationand heat storage capacity. Such energy management is described in U.S.Pat. No. 5,501,268 which recommends plasterboard containing latent heatstorage materials for this purpose. As latent heat storage material, aparaffin mixture is incorporated into the plasterboard. Precise detailsof the way in which it is added are not given.

[0008] U.S. Pat. No. 4,988,543 discusses the opportunities and problemsin the incorporation of latent heat storage materials in plasterboard.Thus, macrocapsules could be located between the outer paperboard layerson the gypsum plaster mix. It is likewise possible for macrocapsules tobe applied to the reverse side of the paperboard. It is conceivable thatsmall spheres could be impregnated with latent heat storage materialsand these spheres could be incorporated into the gypsum plaster mix orthe latent heat storage materials could be mixed directly with thegypsum plaster mix. Finally, the entire, fabricated plasterboard couldbe impregnated with latent heat storage materials. U.S. Pat. No.4,988,543 teaches that the use of capsules or spheres reduces theinternal binding forces of the board. Likewise, processes in which thegypsum plaster is mixed directly with the latent heat storage materialsare critical since adhesion problems with the paper also occur here. Asa solution, U.S. Pat. No. 4,998,543 proposes spraying one side of theplasterboard with latent heat storage materials.

[0009] In the case of large areas of plasterboard which have beentreated with unencapsulated latent heat storage materials, there is arisk of oil emissions into the air of the room. Furthermore, the latentheat storage materials in the liquid state start to flow slowly withinthe plasterboard, resulting in the long term in nonuniform distribution,in particular on the surface, known as “sweating”, which likewise has anadverse effect on the stability of the boards.

[0010] It is an object of the present invention to find a way ofincorporating latent heat storage materials into gypsum plasterboardwhile avoiding the abovementioned disadvantages.

[0011] We have found that this object is achieved by the use ofmicrocapsules comprising latent heat storage materials as capsule corein plasterboard.

[0012] Microcapsules are particles comprising a capsule core consistingpredominantly, to an extent of more than 95% by weight, of latent heatstorage materials and a polymer as capsule wall. The capsule core issolid or liquid depending on the temperature. The mean particle size ofthe capsules is from 0.5 to 100 μm, preferably from 1 to 80 μm, inparticular from 1 to 50 μm. Latent heat storage materials are generallylipophilic substances which have their solid/liquid phase transition inthe temperature range from −20 to 120° C.

[0013] Examples of suitable substances are:

[0014] aliphatic hydrocarbon compounds such as saturated or unsaturatedC₁₀-C₄₀-hydrocarbons which are branched or preferably linear, e.g.n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane,n-nonadecane, n-eicosane, n-heneicosane, n-docosane, n-tricosane,n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane, n-octacosane,and cyclic hydrocarbons, e.g. cyclohexane, cyclooctane, cyclodecane;

[0015] aromatic hydrocarbon compounds such as benzene, naphthalene,biphenyl, o- or n-terphenyl, C₁-C₄₀-alkyl-substituted aromatichydrocarbons such as dodecylbenzene, tetradecylbenzene,hexadecylbenzene, hexylnaphthalene or decylnaphthalene;

[0016] saturated or unsaturated C₆-C₃₀-fatty acids such as lauric,stearic, oleic or behenic acid, preferably eutectic mixtures of decanoicacid with, for example, myristic, palmitic or lauric acid;

[0017] fatty alcohols such as lauryl, stearyl, oleyl, myristyl and cetylalcohols, mixtures such as coconut fatty alcohol and the oxo alcoholsobtained by hydroformylation of α-olefins and further reactions;

[0018] C₆-C₃₀-fatty amines such as decylamine, dodecylamine,tetradecylamine or hexadecylamine;

[0019] esters such as C₁-C₁₀-alkyl esters of fatty acids, e.g. propylpalmitate, methyl stearate or methyl palmitate, and preferably theireutectic mixtures or methyl cinnamate;

[0020] natural and synthetic waxes such as montanic acid waxes, montanicester waxes, carnauba wax, polyethylene wax, oxidized waxes, polyvinylether wax, ethylene-vinyl acetate wax or hard waxes from Fischer-Tropschprocesses;

[0021] halogenated hydrocarbons such as chloroparaffin, bromooctadecane,bromopentadecane, bromononadecane, bromoeicosane, bromodocosane.

[0022] Mixtures of these substances are also suitable as long as themelting point is not reduced to outside the desired range or the heat offusion of the mixture becomes too low for effective use.

[0023] For example, the abovementioned halogenated hydrocarbons can beincorporated as flame retardants. It is also possible to add flameretardants such as bis(pentabromophenyl) oxide, bis(tetrabromophenyl)oxide, antimony oxide or flame retardant additives described in U.S.Pat. No. 4,797,160.

[0024] Furthermore, it is advantageous to add compounds which aresoluble in the substances which form the capsule core to the substancesso as to prevent the depression of the freezing point which sometimesoccurs in the case of the nonpolar substances. It is advantageous touse, as described in U.S. Pat. No. 5,456,852, compounds which have amelting point which is from 20 to 120° C. higher than that of the actualcore substance. Suitable compounds are the fatty acids, fatty alcohols,fatty amides and aliphatic hydrocarbon compounds mentioned above aslipophilic substances.

[0025] The lipophilic substances are selected according to thetemperature range in which heat is to be stored. For example, for heatstorage materials in building materials in Europe, preference is givento using lipophilic substances whose solid/liquid phase transition is inthe temperature range from 0 to 60° C. Thus, individual materials ormixtures having transformation temperatures of from 0 to 25° C. aregenerally chosen for exterior applications, while materials havingtransformation temperatures of from 15 to 30° C. are generally chosenfor interior applications. In the case of solar applications inconjunction. with building materials as storage medium or for avoidingoverheating in the case of transparent thermal insulation, as describedin EP-A 333 145, transformation temperatures of from 30 to 60° C. areespecially useful. It is, for example, advantageous to use alkanemixtures as are obtained as industrial distillate and are commerciallyavailable as such.

[0026] As polymers for the capsule wall, it is in principle possible touse the materials known for the microcapsules in carbonless copyingpaper. It is thus possible, for example, to encapsulate the latent heatstorage materials in gelatin together with other polymers by the methodsdescribed in GB-A 870476, U.S. Pat. No. 2,800,457, U.S. Pat. No.3,041,289.

[0027] Preferred wall materials are thermoset polymers, because of theirvery good aging stability. For the purposes of the present invention,thermoset polymers are wall materials which, owing to their high degreeof crosslinking, do not soften but instead decompose-at hightemperatures. Suitable thermoset wall materials are, for example,formaldehyde resins, polyureas and polyurethanes and also highlycrosslinked methacrylic ester polymers.

[0028] Formaldehyde resins are reaction products of formaldehyde with

[0029] triazines such as melamine,

[0030] carbamides such as urea,

[0031] phenols such as phenol, m-cresol and resorcinol,

[0032] amino and amido compounds such as aniline, p-toluenesulfonamide,ethylenurea and guanidine,

[0033] or mixtures thereof.

[0034] Preferred formaldehyde resins are urea-formaldehyde resins,urea-resorcinol-formaldehyde resins, urea-melamine resins andmelamine-formaldehyde resins. Preference is likewise given to theC₁-C₄-alkyl ethers, in particular methyl ethers, of these formaldehyderesins and also their mixtures with these formaldehyde resins.Particular preference is given to melamine-formaldehyde resins and/ortheir methyl ethers.

[0035] In the processes known from carbonless copying paper, the resinsused are prepolymers. The prepolymer is still soluble in the aqueousphase and during the course of polycondensation migrates to theinterface and encloses the oil droplets. Microencapsulation processesusing formaldehyde resins are generally known and are described, forexample, in EP-A-562 344 and EP-A-974 394.

[0036] Capsule walls comprising polyureas and polyurethanes are likewiseknown from carbonless copying paper. The capsule walls are formed byreaction of reactants bearing NH₂ groups or OH groups with diisocyanatesand/or polyisocyanates. Examples of suitable isocyanates are ethylenediisocyanate, tetramethylene 1,4-diisocyanate, hexamethylene1,6-diisocyanate and tolylene 2,4- and 2,6-diisocyanate. Furtherpolyisocyanates which may be mentioned are derivatives having a biuretstructure, polyuretonimines and isocyanurates. Possible reactants are:hydrazine, guanidine and its salts, hydroxylamine, diamines andpolyamines and amino alcohols. Such interfacial polyaddition processesare known, for example, from U.S. Pat. No. 4,021,595, EP-A 0 392 876 andEP-A 0 535 384.

[0037] Preference is given to microcapsules whose capsule wall is ahighly crosslinked methacrylic ester polymer. The degree of crosslinkingis achieved using a proportion of crosslinker of ≧10% by weight, basedon the total polymer.

[0038] The walls of the preferred microcapsules are built up from 30 to100% by weight, preferably from 30 to 95% by weight, of one or moreC₁-C₂₄-alkyl esters of acrylic acid and/or methacrylic acid as monomersI. In addition, the microcapsule walls can be built up from up to 80% byweight, preferably from 5 to 60% by weight, in particular from 10 to 50%by weight, of one or more bifunctional or polyfunctional monomer asmonomer II which is insoluble or sparingly soluble in water, and up to40% by weight, preferably up to 30% by weight, of other monomers III.

[0039] Suitable monomers I are C₁-C₂₄-alkyl esters of acrylic acidand/or methacrylic acid. Particularly preferred monomers I are methylacrylate, ethyl acrylate, n-propyl acrylate and n-butyl acrylate and/orthe corresponding methacrylates. Preference is given to isopropylacrylate, isobutyl acrylate, sec-butyl acrylate and tert-butyl acrylateand the corresponding methacrylates. Mention may also be made ofmethacrylonitrile. In general, the methacrylates are preferred.

[0040] Suitable monomers II are bifunctional or polyfunctional monomerswhich are insoluble or sparingly soluble in water but have a good tolimited solubility in the lipophilic substance. For the purposes of thepresent invention, sparing solubility is a solubility of less than 60g/l at 20° C.

[0041] For the purposes of the present invention, bifunctional orpolyfunctional monomers are compounds which have at least 2nonconjugated ethylenic double bonds.

[0042] Particular mention may be made of divinyl and polyvinyl monomerswhich effect crosslinking of the capsule wall during the polymerization.

[0043] Preferred bifunctional monomers are diesters of diols withacrylic acid or methacrylic acid, also the diallyl and divinyl ethers ofthese diols.

[0044] Preferred divinyl monomers are ethanediol diacrylate,divinylbenzene, ethylene glycol dimethacrylate, 1,3-butylene glycoldimethacrylate, methallylmethacrylamide and allyl methacrylate.Particular preference is given to propanediol diacrylate, butanedioldiacrylate, pentanediol diacrylate and hexanediol diacrylate or thecorresponding methacrylates.

[0045] Preferred polyvinyl monomers are trimethylolpropane triacrylateand trimethacrylate, pentaerythritol triallyl ether and pentaerythritoltetraacrylate.

[0046] Possible monomers III are other monomers; preference is given tomonomers IIIa such as styrene, α-methylstyrene, α-methylstyrene,butadiene, isoprene, vinyl acetate, vinyl propionate and vinylpyridine.

[0047] Particular preference is given to the water-soluble monomersIIIb, e.g. acrylonitrile, methacrylamide, acrylic acid, methacrylicacid, itaconic acid, maleic acid, maleic anhydride, N-vinylpyrrolidone,2-hydroxyethyl acrylate and methacrylate andacrylamido-2-methylpropanesulfonic acid. In addition, mention may bemade of, in particular, N-methylolacrylamide, N-methylolmethacrylamide,dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate.

[0048] The microcapsules suitable for use according to the presentinvention can be produced by in-situ polymerization. The preferredmicrocapsules and their production are known from EP-A-457 154, which ishereby expressly incorporated by reference. Thus, the microcapsules areproduced by preparing a stable oil-in-water emulsion from the monomers,a free-radical initiator, a protective colloid and the lipophilicsubstance to be encapsulated, with these being present as disperse phasein the emulsion. The proportion of oil phase in the oil-in-wateremulsion is preferably from 20 to 60% by weight.

[0049] The polymerization of the monomers is subsequently triggered byheating, and the resulting polymers form the capsule wall which enclosesthe lipophilic substance.

[0050] In general, the polymerization is carried out at from 20 to 100°C., preferably from 40 to 80° C. The dispersion temperature andpolymerization temperature should naturally be above the melting pointof the lipophilic substances, so that free-radical initiators whosedecomposition temperature is above the melting point of the lipophilicsubstance may be chosen.

[0051] The reaction times of the polymerization are normally from 1 to10 hours, usually from 2 to 5 hours.

[0052] The polymerization process is generally carried out by dispersinga mixture of water, monomers, protective colloids, the lipophilicsubstances, free-radical initiators and, if desired, regulators eitherin succession or simultaneously and, while stirring vigorously, heatingthe dispersion to the decomposition temperature of the free-radicalinitiators. The polymerization rate can be controlled by selection ofthe temperature and of the amount of free-radical initiator. Thereaction is advantageously started by increasing the temperature to astart temperature and the polymerization is controlled by increasing thetemperature further.

[0053] After reaching the final temperature, the polymerization isadvantageously continued for a time of up to about 2 hours to reduce theresidual monomer contents.

[0054] Subsequent to the actual polymerization reaction to a conversionof from 90 to 99% by weight, it is generally advantageous tosubstantially free the aqueous microcapsule dispersions ofodor-imparting substances, e.g. residual monomers and other volatileorganic constituents. This can be achieved in a manner known per se byphysical means by distillation (in particular steam distillation) or bystripping with an inert gas. It can also be achieved by chemical meansas described in WO 9924525, advantageously by redox-initiatedpolymerization as described in DE-A-4 435 423, DE-A-4419518 and DE-A-4435 422.

[0055] In this way, microcapsules having a mean particle size (z-mean,determined by pseudoelastic, dynamic light scattering) in the range from0.5 to 100 μM can be produced. Capsules of this-size are preferred foruse according to the present invention.

[0056] Preferred protective colloids are water-soluble polymers, sincethese reduce the surface tension of water from a maximum of 73 mN/m tofrom 45 to 70 mN/m and thus ensure the formation of closed capsule wallsand of microcapsules having preferred particle sizes of from 1 to 30 μm,preferably from 3 to 12 μm.

[0057] In general, the microcapsules are produced in the presence of atleast one organic protective colloid which may be either anionic oruncharged. Anionic and nonionic protective colloids can also be usedtogether. Preference is given to using inorganic protective colloids, ifdesired in admixture with organic protective colloids.

[0058] Uncharged organic protective colloids-are cellulose derivativessuch as hydroxyethylcellulose, carboxymethylcellulose andmethylcellulose, polyvinylpyrrolidone, copolymers of vinylpyrrolidone,gelatin, gum arabic, xanthan gum, sodium alginate, casein, polyethyleneglycols, preferably polyvinyl alcohol and partially hydrolyzed polyvinylacetates.

[0059] To improve the stability of the emulsions, anionic protectivecolloids can be added. The use of anionic protective colloids isparticularly important when the dispersion has a high content ofmicrocapsules, since formation of agglomerated microcapsules can occurwithout an additional ionic stabilizer. These agglomerates reduce theyield of usable microcapsules-if the agglomerates comprise smallcapsules having a diameter of from 1 to 3 μm, and they increase thesusceptibility to fracture if the agglomerates are larger than about 10μm.

[0060] Suitable anionic protective colloids are polymethacrylic acid andcopolymers of sulfoethyl acrylate and methacrylate, sulfopropyl acrylateand methacrylate, N-(sulfoethyl)maleimide, 2-acrylamido-2-alkylsulfonicacids, styrenesulfonic acid or vinylsulfonic acid.

[0061] Preferred anionic protective colloids are naphthalenesulfonicacid and naphthalenesulfonic acid-formaldehyde condensates andespecially polyacrylic acids and phenolsulfonic acid-formaldehydecondensates.

[0062] The anionic protective colloids are generally used in amounts offrom 0.1 to 10% by weight, based on the aqueous phase of the emulsion.

[0063] Preference is given to inorganic protective colloids, known asPickering systems, which make it possible to stabilize very fine solidparticles and are insoluble but dispersible in water or are insolubleand nondispersible in water but can be wetted by the lipophilicsubstance.

[0064] Microencapsulation processes using such Pickering systems aredescribed, for example, in U.S. Pat. No. 3,615,972 and U.S. Pat. No4,016,110.

[0065] A Pickering system can consist of solid particles alone oradditionally of auxiliaries which improve the dispersibility of theparticles in water or improve the ability of the lipophilic phase to wetthe particles. These auxiliaries are, for example, nonionic, anionic,cationic or zwitterionic surfactants or polymeric protective colloids asare described above or below. Buffer substances can additionally beadded to set particular pH values of the aqueous phase which areadvantageous in each case.

[0066] This can reduce the water solubility of the fine particles andincrease the stability of the emulsion. Customary buffer substances arephosphate buffers, acetate buffers and citrate buffers.

[0067] The fine, solid particles can be metal salts, e.g. salts, oxidesand hydroxides of calcium, magnesium, iron, zinc, nickel, titanium,aluminum, silicon, barium and manganese. Mention may be made ofmagnesium hydroxide, magnesium carbonate, magnesium oxide, calciumoxalate, calcium carbonate, barium carbonate, barium sulfate, titaniumdioxide, aluminum oxide, aluminum hydroxide and zinc sulfide. Silicates,bentonite, hydroxyapatite and hydrotalcite may likewise be mentioned.Particular preference is given to finely divided silicas, magnesiumpyrophosphate and tricalcium phosphate.

[0068] The Pickering systems can either be added initially to theaqueous phase, or they can be added to the stirred emulsion ofoil-in-water. Some fine, solid particles are prepared by precipitation.Thus, magnesium pyrophosphate is prepared by combining aqueous solutionsof sodium pyrophosphate and magnesium sulfate.

[0069] In general, the pyrophosphate is prepared immediately beforedispersion by combining an aqueous solution of an alkali metalpyrophosphate with at least the stoichiometrically required amount of amagnesium salt, with the magnesium salt being able to be present insolid form or as an aqueous solution. In a preferred embodiment, themagnesium pyrophosphate is prepared by combining aqueous solutions ofsodium pyrophosphate (Na₄P₂O₇) and magnesium sulfate (MgSO₄7H₂O). Thefinely divided silicas can be dispersed in water as fine, solidparticles. However, it is also possible to use colloidal dispersions ofsilica in water. The colloidal dispersions are alkaline, aqueousmixtures of silica. In the alkaline pH range, the particles are swollenand stable in water. For these dispersions to be used as a Pickeringsystem, it is advantageous for the pH of the oil-in-water emulsion to beadjusted to from 2 to 7 by means of an acid.

[0070] The inorganic protective colloids are generally used in amountsof from 0.5 to 15% by weight, based on the aqueous phase. In general,the uncharged organic protective colloids are used in amounts of from0.1 to 15% by weight, preferably from 0.5 to 10% by weight, based on theaqueous phase.

[0071] The dispersion conditions for preparing the stable oil-in-wateremulsion are preferably selected in a manner known per se so that themicrocapsules have a mean diameter of from 1 to 35 μm, preferably from 3to 10 μm.

[0072] The microcapsules can be incorporated as a powder or as adispersion into the plasterboard. Here, preference is given toincorporatingfrom 5 to 40% by weight, in particular from 20 to 35% byweight, of microcapsules, based on the total weight of the plasterboard(dry basis).

[0073] The plasterboard of the present invention comprises a gypsumplaster core and paperboard sheets applied to both sides. Plasterboardis usually produced by introducing an aqueous plaster of Paris mixdiscontinuously or continuously between two paperboard sheets having acellulose basis, thus producing boards. The plaster of Paris mix is, asis generally known, produced by continuous addition of calcium sulfateβ-hemihydrate to water containing additives while mixing continually.The microcapsules can either be added together with the calcium sulfateor they can be present beforehand as an aqueous dispersion. The aqueousdispersion is preferably mixed with the calcium sulfate, since this canbe metered particularly well in this way. The plaster of Paris mixobtained is applied to the paperboard sheets, for example sprayed on,and covered with paperboard.

[0074] During initial curing, the plasterboards are shaped in a press toform strips having, for example, a width of 1.2-1.25 m and a thicknessof 9.25, 12.5, 15.0, 18.0 or 25 mm. These strips harden within a fewminutes and are cut into boards. In this state, one third of the weightof the boards is generally still free water. To remove the remainingwater, the boards are subjected to a heat treatment at about 250° C.This is carried out, for example, in tunnel driers. The plasterboardsobtained in this way have a density of 750-950 kg/m³.

[0075] Preference is given to plasterboard in which the paperboard usedhas a thickness of from 0.2 to 1 mm and/or a grammage of from 100 to 500g/m².

[0076] It is usual to use paperboard having a grammage of about300 g/m²for plasterboard. Paperboard of this type is usually produced in aplurality of layers, with the final layer representing the outercovering layer of the paperboard, and has a grammage of from 10 to100g/m², preferably from 30 to 70 g/m².

[0077] Apart from this conventional paperboard, it is also possible touse paperboard sheets in which the outer covering layers of bothpaperboard sheets, the intermediate layers or the entire paperboardsheets contain 10-90% by weight, preferably 40-70% by weight, ofpolyolefin fibrils.

[0078] The heat treatment at about 250° C. required for the productionof the plasterboard results in a surface temperature on the boards afterevaporation of the water which is sufficient to plasticize thepolyolefin fibrils and conglutinate with the other paperboardcomponents. This results in substantial closure of the pores on theouter layer of the paperboard and the surface of the plasterboardbecomes water-resistant. This pore-closing conglutination occurs onlywhen all the water has evaporated, since before this the temperaturecannot exceed 100° C. in the board because of generation of water vapor.Following the heat treatment by a hot gas treatment with a gas at from130° to 300° C., preferably from 1400 to 200° C., can improve the effectfurther. The treatment with hot gas can also, regardless of the heattreatment during manufacture, be carried out at a later point in time.

[0079] Instead of a hot gas treatment, it is also possible to use asmooth or embossed roller whose temperature is above the softening pointof the polyolefin fibrils.

[0080] In one embodiment, the plasterboard is produced using paperboardwhose total mass or the individual layers, but preferably the outercovering layer, comprises a mixture of 90-10% by weight, preferably60-30% by weight, of cellulose fibers and 10-90% by weight, preferably40 - 70% by weight, of polyolefin fibrils, based on the dry weight.

[0081] Polyolefin fibrils are polyolefin fibers which are, for example,produced by a decompression evaporation process in which a pressurized,superheated emulsion comprising

[0082] a) a solution of a polyolefin in a low-boiling solvent and

[0083] b) an aqueous solution of a hydrophilicizing agent is sprayedthrough a nozzle into a low-pressure zone, with the hydrophilicizingagent being used in an amount of 0.2-3% by weight, preferably 0.5-2% byweight, based on the polyolefin. Particularly useful polyolefins arepolyethylene having a reduced specific viscosity of from 0.3 to 30 dl/g,preferably from 0.7 to 10 dl/g (determined by the method of H. Weslau,Kunststoffe 49 (1959), p. 230) and a density of from 0.93 to 0.97 g/cm³,and polypropylene. These polyolefins may contain small amounts ofcomonomers having from 3 to 6 carbon atoms.

[0084] Suitable hydrophilicizing agents encompass, in principle, allknown types of emulsifiers, but preference is given to using polymerichydrophilicizing agents containing amine groups, amide groups, carboxylgroups and/or hydroxyl groups. Very good results are obtained, inparticular, using polyvinyl alcohol having a solution viscosity(measured in a 4% strength solution in water at 20° C.) of from 4 to 70cP and a degree of saponification of from 80 to 99.5%.

[0085] Methods of producing polyolefin fibrils may be found, forexample, in DE-A-2718322.

[0086] It has been found that paperboard containing polyolefin fibrilscan be processed particularly advantageously with themicrocapsule-containing gypsum plaster and displays particularly goodbinding forces.

[0087] In place of paperboard having a cellulose basis, it is alsopossible to use alternative, fibrous sheets to cover both sides of theplasterboard of the present invention. Alternative materials are polymerfibers made of, for example, polypropylene, polyester, polyamide,polyacrylates, polyacrylonitrile and the like. Glass fibers are alsosuitable. The alternative materials can be used as woven fabrics and asnonwovens.

[0088] Such plasterboards are known, for example, from U.S. Pat. No.4,810,569, U.S. Pat. No. 4,195,110 and U.S. Pat. No. 4,394,411.

[0089] High proportions of microcapsules in the gypsum plaster cansometimes lead to hydrophobicization of the gypsum-based buildingmaterial. This can sometimes also result in poorer adhesion to thesubstrates onto which these modified gypsum plasters are applied, forexample adhesion to the paperboard can be impaired.

[0090] It has now been found that stronger adhesion to substrates suchas paperboard can be achieved by addition of natural and/or syntheticpolymers. Suitable water-soluble polymers are: starches and starchethers, relatively high molecular weight methylcelluloses and othercellulose derivatives, guar gum derivatives, thermoplastic dispersionpowders and liquid dispersions based on vinyl acetate, ethylene-vinylacetate, vinyl propionate, styrene-butadiene, styrene acrylate and pureacrylate. The amount of the polymers added is from 0,1 to 5% by weight,based on the total dry weight of plaster of Paris and latent heatstorage material. The polymers mentioned improve not only the adhesionto the substrate, i.e. the paperboard, but usually also increase thefracture strength and flexural strength of the plasterboard of thepresent invention. Preference is given to plasterboard whose gypsumplaster contains from 0.1 to 5% by weight, based on the total dry weightof gypsum plaster and latent heat storage material, of water-solublepolymers. Furthermore, it is advantageous to add water retention aidsand/or thickeners as further additives to the gypsum plastercompositions. Examples are polyvinyl alcohol, cellulose derivatives suchas hydroxyethylcellulose, hydroxypropylcellulose,carboxymethylcellulose, polyacrylic acid and copolymers of acrylic acid,e.g. polyethylene-co-acrylic acid, polymaleic acid-co-acrylic acid,polyisobutylene-co-acrylic acid and acrylic acid-rich polymerdispersions with styrene or acrylic esters or vinyl acetate, as are usedas thickeners for, for example, paper finishing. The water retentionaids and/or thickeners are usually used in amounts of from 0.05 to 2% byweight, based on the total dry weight of gypsum plaster and latent heatstorage material. The gypsum plaster which has been modified in this waydisplays excellent processing properties. For this reason, preference isgiven to plasterboard whose gypsum plaster contains from 0.05 to 2% byweight of water retention aid or thickener, based on the total dryweight of gypsum plaster and latent heat storage material.

[0091] The present invention further provides a process for producingplasterboard comprising a gypsum plaster core and paperboard sheetsapplied to both sides, by introducing an aqueous slurry of plaster ofParis between two paperboard sheets having a cellulose basis and heattreating the boards formed in this way, wherein the slurry of plaster ofParis comprises microcapsules/calcium sulfate hemihydrate in a weightratio of from 5/95 to 40/60.

[0092] The plasterboard of the present invention has good heat storageproperties. The boards have good mechanical strength and display goodstorage properties. Furthermore, no outward migration of heat storagewaxes is observed.

[0093] The plasterboard is suitable for wall and ceiling elements forthe interior finishing of buildings. The following examples illustratethe invention.

[0094] The percentages in the examples are by weight. The K valuesreported in the examples were determined by the method of H.Fikentscher, Cellulose-Chemie, vol. 13, 58-64 and 71-74 (1932), in 1%strength aqueous solution at 25° C. Production of the microcapsulesAqueous phase:

[0095] 930 g of water

[0096] 263 g of a 30% strength colloidal dispersion of SiO₂ in water ata pH of 9.8 (12 nm, 240 m²/g) 18.2 g of a 20% strength aqueous solutionof a polymer derived from 59% of 2-acrylamido-2-methylpropanesulfonicacid sodium salt, 20% of acrylic acid, 20% of methyl acrylate and 1% ofstyrene, K=69

[0097] 10.5 g of a 2.5% strength aqueous solution of potassiumdichromate

[0098] Oil phase:

[0099] 1100 g of C₁₈-C₂₀-alkane (industrial distillate)

[0100] 129.5 g of methyl methacrylate

[0101] 57.4 g of butanediol diacrylate

[0102] 1.9 g of ethylhexyl thioglycolate

[0103] 2.3 g of t-butyl perpivalate Feed stream 1: 2.73 g of t-butylhydroperoxide, 70% strength in water Feed stream 2: 0.84 g of ascorbicacid, 0.061 g of NaOH, 146 g of H₂O

[0104] The above aqueous phase was placed in a reaction vessel at roomtemperature and the pH was adjusted to 7 by means of 14 g of 10%strength hydrochloric acid. After addition of the oil phase, the latterwas dispersed by means of a high-speed stirrer at 4200 rpm and the pHwas adjusted to 4 by means of 15 g of 10% strength hydrochloric acid.After the mixture had been dispersed for 40 minutes, a stable emulsionhaving a particle diameter of from 2 to 8 μm was obtained. Whilestirring with an anchor stirrer, the emulsion was heated to 56° C. overa period of 4 minutes, to 58° C. over a further period of 20 minutes, to71° C. over a further period of 60 minutes and to 85° C. over a furtherperiod of 60 minutes. The resulting microcapsule dispersion was cooledto 70° C. while stirring and feed stream 1 was added. While stirring at70° C., feed stream 2 was metered in over a period of 80 minutes. Themixture was subsequently cooled. The resulting microcapsule dispersionhad a solids content of 45.7% and a mean particle size D(4.3) =4.22 μm.

[0105] The dispersion could be dried without problems in a laboratoryspray drier using a two-fluid nozzle and cyclone precipitation at aninlet temperature of the hot gas of 130° C. and an exit temperature ofthe powder from the spray drier of 70° C. On heating in a differentialscanning calorimeter at a heating rate of 1 K/minute, microcapsuledispersion and powder displayed a melting point in the range from 26.5to 29.5° C. and a transformation enthalpy of 130 J/g of alkane mixture.

[0106] Production of the plasterboard

[0107] A mixture of 750 g of plaster of Paris (calcium sulfateβ-hemihydrate), 250 g of microcapsule powder containing latent heatstorage material from the example above and 2 g of Culminal MC 7000 PF(methylcellulose, from Aqualen) is mixed with 850 g of water to give auniform slurry and the mixture is immediately poured onto a sheet ofpaperboard having a grammage of 300 g/m² and covered with a second sheetof paperboard and smoothed to a thickness of 12 mm. After asolidification time of 10 minutes, the board is dried at 200° C. in adrying oven for 15 minutes.

[0108] The plasterboard manufactured in this way has a normalappearance, the microcapsules are not broken and the measured heatstorage capacity at 20-30° C. corresponds to the calculated proportionof latent heat storage material added.

1-12. (Canceled)
 13. A plasterboard which comprises microcapsulescomprising latent heat storage materials as capsule core.
 14. Aplasterboard as claimed in claim 13, wherein the latent heat storagematerials are lipophilic substances which have their solid/liquid phasetransition in the temperature range from −20 to 120° C.
 15. Aplasterboard as claimed in claim 13, wherein the capsule wall of themicrocapsules is a thermoset polymer.
 16. A plasterboard as claimed inclaim 13, wherein the capsule wall of the microcapsules is a highlycrosslinked methacrylic ester polymer.
 17. A plasterboard as claimed inclaim 13, wherein the capsule wall of the microcapsules is obtainable byfree-radical polymerization of a monomer mixture comprising from 30 to100% by weight, based on the total weight of the monomers, of one ormore C₁-C₂₄-alkyl esters of acrylic acid and/or methacrylic acid(monomer I), from 0 to 80% by weight, based on the total weight of themonomers, of one or more bifunctional or polyfunctional monomers(monomers II) which are insoluble or sparingly soluble in water and from0 to 40% by weight, based on the total weight of the monomers, of othermonomers (monomers III).
 18. A plasterboard as claimed in claim 13,wherein the mean particle size of the microcapsules is from 0.5 to 100mm.
 19. A plasterboard as claimed in claim 13 which comprises 5-40% byweight of microcapsules, based on the weight of the plasterboard.
 20. Aplasterboard as claimed in claim 13, wherein the paperboard used has athickness of from 0.2 to 1 mm and/or a grammage of from 100 to500 g/m².21: A plasterboard as claimed in claim 13, wherein the fibrous sheets tocover both sides of the plasterboard are made of polymer fibres.
 22. Aplasterboard as claimed in claim 13, wherein the fibrous sheets to coverboth sides of the plasterboard are made of glass fibers.
 23. A processfor producing plasterboard as claimed in claim 13 comprising a gypsumplaster core and paperboard sheets applied to both sides, by introducingan aqueous slurry of plaster of Paris between two paperboard sheetshaving a cellulose basis and heat treating the boards formed in thisway, wherein the slurry of plaster of Paris comprisesmicrocapsules/calcium sulfate hemihydrate in a weight ratio of from 5/95to 40/60.
 24. A process for producing plasterboard as claimed in claim13 comprising a gypsum plaster core and polymer- or glass-fiber sheetsto cover both sides of the plasterboard, by introducing an aqueousslurry of plaster of Paris between polymer- or glass-fiber sheets andheat treating the boards formed in this way, wherein the slurry ofplaster of Paris comprises microcapsules/calcium sulfate hemihydrate ina weight ratio of from 5/95 to 40/60.